Katja Woth & Hans von Storch

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1 Katja Woth & Hans von StorchClimate change and North Sea storm surge extremes - an ensemble study (PRUDENCE)Katja Woth & Hans von StorchInstitute for Coastal ResearchGKSS Research CenterGeesthacht, GermanyAbstract Reference Number: 251Abstract Title: Climate change and North Sea storm surge extremes - an ensemble study (PRUDENCE)Paper Number: A51F-01Presentation Type: OralPresentation Date: Friday, 17 DecemberLocation: 3016Starting Time: 08:04Time allotted: Time Allotted: 12 minutesClimate change and North Sea storm surge extremes - an ensemble study (PRUDENCE)Hans von Storch & Katja WothPossible changes in North Sea storm surge climate are studied in a systematic manner.Following up on previous studies, we use a tide-surge model to derive storm surge climateand extremes from atmospheric conditions under present-day and enhanced greenhouse gasconditions. Results for modeled storm surges obtained by using regional model output fromfour RCMs, namely CLM (GKSS), RCAO (SMHI), REMO5 (MPI) and HIRHAM (DMI) arepresented.The atmospheric regional simulations were prepared within the EU project PRUDENCE. Theresearch strategy of PRUDENCE is to compare simulations of different regional models(RCMs) driven by the same global control and climate change simulations. These globalconditions, representative for and were prepared by the Hadley Centerbased on the IPCC A2 SRES scenario. The effect on windiness of the enhanced greenhousegas conditions, projected by these four regional climate models was in all cases similar,namely a moderate increase of high wind speeds in most parts of the North Sea during winter.These simulated surface wind and pressure data have been used to run a storm surge model.We show the expected storm-related changes in different storm surge parameters. Forinstance, the largest increase of high water levels, defined as the 99.5%ile during wintersampled every half hour would have to be expected along the southern and eastern North Seacoast, with maximum values of around 30 cm, which is beyond the range of normal year-toyearvariations. Similar results can be found for all four experiments. Together with theexpected rise of mean water levels of 40 cm by IPCC (2001), the total increase is 70 cm at theend of the 21st century under the assumptions of the rather severe A2 scenario. If an ECHAMscenarioA2 is used, quantitatively similar results are obtained, but in that case there are alsosignificant increases along parts of the UK coast.

5 Comparison of wind speed statistics with in-situ data: RCM is skillful in describing marine wind statisticsNot assimilated into NCEP (Ionic Sea)These plots are the quantile-quantile diagrams (REMO & NCEP Vs Observations) for 10-m wind speed at 2 buoys station. The first one is an Atlantic offshore buoy (ZBGSO, located at48.7N,12.40W), already assimilated by NCEP. The second one shows results from a Mediterranean buoy (ZATOS, located at 39.96N, 24.72E, Aegean Sea), whose data have NOT been previously assimilated by NCEP.

11 SREs emission scenarios: Impact on global sea levelAccording to scenario A2 and the specific set of GCM / RCMs, water level may rise in extreme situations by as much as40 cm + 30 cm = 70 cmalong the German North Sea coast.IPCC, 2001SREs emission scenarios: Impact on global sea level

12 ConclusionsDynamical models have been demonstrated to be a useful tool to describe the statistics, and changes thereof, of wind-related phenomena in coastal seas – wind force, storm surge, coastal currents and ocean waves.An ensemble of regionalizations, derived from one global A2 scenario, results in rather similar changes of regional wind over the North sea and the associated change of surge levels.Along the German North Sea coast, water levels may rise by up to 70 cm - of which 40 cm are due to mean sea level rise and 30 cm to different storm patterns.